Study On Characteristics Of The Compression Wave Propagating Through High-speed Railway With Side Branches

When a high-speed train enters a tunnel, a compression wave is formed ahead of the train,which propagates along the tunnel at a nearly sonic speed. And when it reaches the exit of thetunnel, much of the compression wave is reflected back to the train as a expansion wave and alittle part of it as the impulsive wave is radiated from the portal toward the outside, thisimpulsive wave is called a "micro-pressure wave". The micro-pressure wave causes anexplosive noise and/or an abrupt rattling of the window frames or shutters of houses near thetunnel exit, which seriously affects the inhabitants near the tunnel exit. The magnitude ofmicro-pressure wave is proportional to the maximum time rate of pressure change of thecompression wave reaching the exit. For this reason, it is very important to clarify thedistortion of waveform of the entry compression wave arrived the exit of tunnel.This paper analyzes the characteristic of the airflow caused by the compression waveinside tunnel and studies the characteristic of the propagation of waveform Arctan+L in thetunnel by the numerical simulation method based on one-dimensional unsteady compressiblenon-isentropic flow model and the method of characteristics. First, the charactics of thecompression waves propagating in tunnel without side branch is studied. The results showthat the maximum of pressure change is scaling as the index of train speed and the value ofthe index in entry portal of tunnel is2, but it is more less than2in the exit portal of tunnelwith more the length of tunnel. The maximum of the rate of the pressure change increaseswith train speed, but the relationships between the maximum of the rate of the pressurechange and the train speed with different tunel length are different. From the result, thereexists a tunnel length at which the maximum of the rate of the pressure change. Secondly,based on the research of Japanese, the relationship of the characteristic of the compressionwaves propagating with the position, the cross-section area and the number of side branch isstudied, the corresponding the maximum of pressure and the maximum of the rate of pressurechange are given at the different train speed and with different tunnel length. These resultsshow that there exist also a tunnel length at which the maximum of the rate of the pressurechange and this tunnel length is shorter than its without side branch in tunnel. The papersumarizes two different tunnel characteristics and give the maximum of pressure and themaximum of pressure change rate in these tunnel.